1. Field of the Invention
The present invention relates to a tilt detector for detecting a tilt which is present between an information reading means for reading recorded information from a recording disk as a recording medium and the recording disk.
2. Description of Related Background Art
For correctly reading recorded information from a recording disk as an optical recording medium, it is necessary to irradiate the recording disk with a reading beam perpendicularly to a recording surface thereof. However, if the recording disk itself warps, the recording disk cannot be irradiated with the reading beam perpendicularly to the recording surface thereof, thereby resulting in a reduction in information reading accuracy.
To avoid this inconvenience, a recorded information reproducing apparatus for reproducing recorded information from such a recording disk is provided with a tilt sensor for detecting a tilt formed between a pickup as an information reading means and the recording disk. The entire pickup is tilted by an angle corresponding to a tilt detected by the tile sensor, or desired signal processing is applied to a read signal read by the pickup in accordance with the detected tilt, thereby preventing information reading accuracy from reducing.
FIG. 1 is a diagram schematically illustrating the configuration of a recorded information reproducing apparatus which is equipped with a tilt sensor 4 for detecting a tilt between a recording disk and a pickup, as mentioned above.
Referring specifically to FIG. 1, a beam generator 41 in the tilt sensor 4 emits divergent light which is irradiated to two different positions on a recording surface of a recording disk 3 rotated or driven by a spindle motor 2. A light detector 42 receives a portion of reflected light produced when the divergent light is irradiated to the recording surface of the recording disk 3, and supplies a subtractor 44 with a first detecting signal having a level corresponding to the amount of received light. A light detector 43, in turn, is disposed at a position which is symmetrical to the light detector 42 with respect to the beam generator 41. The light detector 43 receives a portion of the reflected light produced when the divergent light is irradiated to the recording surface of the recording disk 3, and supplies the subtractor 44 with a second detecting signal having a level corresponding to the amount of received light. The subtractor 44 calculates the difference in level between the first detecting signal and the second detecting signal, and outputs the difference as a tilt error signal. The apparatus is herein on the assumption that the beam generator 41 and the light detectors 42, 43 are disposed on the same parallel surface as a pickup, not shown.
When the recording surface of the recording disk 3 and the pickup is maintained in a parallel relationship, the light detectors 42, 43 receive the same amount of reflected light, causing the subtractor 44 to generate the tilt error signal at "0." On the other hand, if the recording disk 3 is not flat for warp or the like, the light detectors 42, 43 receive different amounts of received light from each other, causing the subtractor 44 to output the tilt error signal corresponding to the difference in the amount of reflected light.
However, if the tilt sensor 4 is equipped in a recorded information reproducing apparatus, there is a problem that the scale of the apparatus becomes larger. Further, there is another problem that high positioning accuracy is required to correctly locate the tilt sensor 4 at a position for maintaining a parallel relationship with the pickup when the tilt sensor 4 is mounted.